This invention relates generally to a method and device for removing dissolved oxygen from fuels and more particularly to a spirally wound membrane for removing dissolved oxygen from liquid hydrocarbon fuels.
Fuel can be utilized as a cooling medium for various systems of an energy conversion device. However, increasing the temperature of fuel also increases the rate at which oxidative reactions occur. The usable cooling capacity of a particular fuel is limited by coke formation and deposition, which is dependent on the amount of dissolved oxygen present within the fuel due to prior exposure to air. Reduction of the amount of dissolved oxygen within the fuel can result in the reduction of coke formed within a fuel delivery system of the energy conversion device.
Decreasing the amount of dissolved oxygen present within fuel reduces the formation of insoluble products referred to as “coke” or “coking”. Reducing the amount of oxygen dissolved within the fuel decreases the rate of coke deposition and increases the maximum allowable temperature. In other words, the less dissolved oxygen within the fuel, the higher the temperature before coke buildup becomes a problem. For many fuels, in order to suppress coke deposition, it is generally agreed that the concentration of dissolved oxygen should be reduced below approximately 2 ppm or approximately three percent of saturation although the degree of de-oxygenation will also depend on the amount of heating the fuel will subsequently undergo. For moderate temperatures, less de-oxygenation would be required and for fuels operating at high temperatures (up to 800 F) dissolved oxygen levels below 2 ppm would be desirable. Fuels that currently have improved coking performance are generally more expensive or require additives, and therefore are not always available.
Known devices for removing dissolved oxygen include a gas-permeable membrane disposed within the fuel system. Fuel passes along the permeable membrane, oxygen molecules in the fuel dissolve into the membrane and then diffuse across it and are removed. A vacuum or oxygen partial pressure differential across the permeable membrane drives oxygen from the fuel, which is unaffected and passes over the membrane.
As is appreciated permeable membranes are difficult to manufacture and are limited in size and construction by sizing and economic factors. Membrane bundles are difficult to scale because performance is highly dependent on spacing and geometry and thus hard to predict. High pressures are also a concern with membrane construction. Further, space and weight are driving factors for any system, and any reduction in space and weight provide immediate benefits to operation.
Accordingly it is desirable to design a permeable membrane system that can remove dissolved oxygen from fuel down to the level required to suppress coke formation, and to configure it such that it efficiently utilizes space, reduces weight, is easily scalable, performs predictably, and can be manufactured economically.